In these days, a technology of measuring a state of a circuit pattern formed on a wafer during a process assumes an important role in a manufacture line of a semiconductor device. Conventionally, most of these measuring technologies are ones that are based on optical microscopes. However, in order to be compatible with miniaturization of semiconductor devices and complication of manufacturing processes in recent year, measurement apparatus based on the electron microscope are being popularized. However, since generally surfaces of circuit patterns are constructed with an insulating film made of SiO2, SiN, a polymer, such as a resist, or the like, there is a problem that, if circuit patterns are measured using charged particles, such as an electron beam, surfaces of semiconductor devices are electrified and accordingly measurement precision may deteriorate. Therefore, in the case where a specimen, such as a semiconductor device, whose surface is prone to be electrified is measured, it is important to control charge of the surface of the specimen in order to prevent degradation in measurement precision. In addition, in the inspection of semiconductor devices, there arise needs of inspection for failures of electric characteristics, such as conduction and non-conduction, that are difficult to detect with optical inspection instruments, and consequently electron beam type inspection instruments are coming into wide use. When this electron beam type inspection instrument detects defects of electric characteristics of the semiconductor device, a circuit pattern formed on a wafer surface is electrified and contrast that becomes manifest thereby is used for the detection. This is called the voltage contrast method and is effective means to detect failures of electric characteristics of semiconductor devices. In order to perform the inspection using this voltage contrast method with excellent repeatability and with high precision, it is necessary to manage charge of a circuit pattern that is a target of inspection. Increase in this control precision directly leads to improvement of detection precision of failures of electric characteristics.
JP-A No. 294345/1998 discloses a processing method for rendering charge of a wide range of areas including a measured area uniform for a time other than acquiring time of an image, as a method for controlling charge of a specimen surface. This processing does not need to be the same as that of a light source used in the measurement, and the processing of rendering charge uniform can be performed by disposing other light sources, such as an electron source, an ion source, a plasma source, and a light source, for uniform processing.
Moreover, JP-A No. 208085/2000 discloses a method for controlling charge using a charge control electrode. This method uses an electron source for a light source for charge processing, and energy of a primary electron is adjusted so that the number of secondary electrons emitted from a specimen may become larger than the number of the primary electrons incident on the specimen. In addition, using the charge control electrode disposed right above the illumination area, a potential difference between the specimen and the electrode is maintained at a desired potential, whereby charge control is conducted.
JP-A No. 173528/2000 discloses a method for controlling charge where a variation in an electrified state of a specimen is sensed by monitoring temporal variation of an acquired voltage contrast image and charge control is conducted by altering illumination energy of a primary electron beam that irradiates the specimen.
In light of improving efficiency of a manufacture process of a semiconductor device, it is preferable that charge control processing is conducted as quickly as possible. In order to increase a processing speed of charge control, a light source that can irradiate a large area at one time using a large current is suitable. Although general electron sources have been proven and guaranteed for their stable operations, many of them operate in an ultra high vacuum (<1×10−6 [Pa]) (for example, the field emission type electron source and the Schottky emission type electron source) or at a temperature of 1000K or higher (for example, LaB6, the W filament type electron source). They are too massive to install separately as a second electron source, and needs a lens etc. to irradiate a large area at one time. As one of electron sources satisfying such requirements, there is a Carbon NanoTube electron source (hereinafter, abbreviated as CNT cathode). JP-A No. 202217/2003 discloses a technology of equalizing charge of a wafer using the CNT cathode.
Naturally it is important to observe or detect an electrified state of a specimen during processing of charge in performing charge processing efficiently. However, observation means suitable for an inspection instrument of a semiconductor device did not exist conventionally. Although there was a surface electrometer as means for observing an electrified state of the specimen surface, the electrometers could not be placed at the same position as a point where charge processing was performed, and consequently it can be used only in a procedure of using the electrometer after charge processing. In this case, since charge processing and potential measurement cannot be conducted simultaneously, whether charge of the surface by charge processing has reached saturation cannot be determined and hence determination as to whether charge processing is completed is impossible. Therefore, it is unsuitable to apply this system to the semiconductor measurement apparatus that is required high-precision ad high-speed charge control. Moreover, although JP-A No. 173528/2000 discloses a technology of detecting an electrified state by monitoring a variation in voltage contrast of an acquired image, it comes with a necessity of performing image processing each time an electrified state is analyzed, and consequently it does not match high-speed of processing. Moreover, since there is the case where charge of a specimen varies in acquiring an image, applying the technology of JP-A No. 173528/2000 to a charge monitor needs a caution.
Moreover, although the above-mentioned JP-A No. 294345/1998 and JP-A No. 202217/2003 discloses a technology of performing charge processing using a charged particle beam source different from the primary electrons as means for realizing charge processing, a technology where an electrified state is observed and charge processing or charge control is performed based on its results is not disclosed.